/Engine/Source/Runtime/Engine/Public/HLSLTree/HLSLTree.h
The HLSLTree module contains classes to build an HLSL AST (abstract syntax tree) This allows C++ to procedurally define an HLSL program. The structure of the tree is designed to be flexible, to facilitate incremental generation from a material node graph Once the tree is complete, HLSL source code may be generated
namespace UE { namespace HLSLTree { enum EDerivativeCoordinate { Ddx, Ddy, } } }